The present invention relates to processes for the preparation of polymers, and more specifically to a bead suspension polymerization and to the polymer formed thereby. In one embodiment, the present invention relates to a suspension polymerization process for producing low ash content polymer beads, that is polymer beads containing low or no residual inorganic contaminants, from at least one monomer comprising providing a reaction medium suitable for conducting said polymerization; forming a suspension agent system in said reaction medium by in situ interaction of at least two components in said reaction medium, for example a metal halide salt and a polar polymer; adding at least one polymerizable monomer compound to the resulting reaction medium having the suspension agent system dispersed therein; and effecting polymerization of the monomer or monomers in the reaction medium to form beads of said polymer. The polymer resin beads produced by the process of the present invention in embodiments are essentially free of inorganic residuals, that is the product contains less than about 100 parts per million of noncombustible inorganic ash residue.
It is known to form resins by bead suspension polymerization. It is also known that suspension agents can be used to stabilize a dispersion of a polymerizable material. A wide variety of suspension agents have been disclosed in the prior art, such as polyvinyl alcohol, gelatin, methyl cellulose, methylhydroxypropyl cellulose, ethyl cellulose, sodium salts of carboxymethylpolyacrylic acid and salts thereof, starch, gum, alginic acid salts, zein, casein, tricalcium phosphate, talc, barium sulfate, bentonite, aluminum hydroxide, ferric hydroxide, titanium hydroxide and thorium hydroxide, reference for example U.S. Pat. Nos. 4,601,968 and 4,609,607, the disclosures of which are totally incorporated herein by reference.
Another method known in the art for forming a suspension involves dispersing a monomer system comprising a polymerizable organic monomer and a polar polymer in a dispersion medium containing a dispersant having a charging polarity opposite to that of the polar polymer. Such a method is disclosed in U.S. Pat. No. 4,592,990.
U.S. Pat. No. 4,659,641 also discloses a process wherein a suspension agent such as tricalcium phosphate is selected to stabilize the mixture. A relatively large amount, about 3 weight percent of total monomer used, of this suspension agent is required.
In a patentability search report the following patents were recited:
U.S. Pat. No. 4,415,644 to Tamaki et al., issued Nov. 15, 1983, discloses a suspension polymerization process employing certain salts, including potassium and sodium iodide as an emulsification-preventing agent, see for example column 3, lines 5 to 11.
U.S. Pat. No. 4,330,460 to Hoffend et al., issued May 18, 1982, discloses a dispersion polymerization process for producing colored toners comprising mixing a colorant with a monomer to form an oil soluble organic phase, mixing the organic phase with an aqueous phase containing a suspending agent and an inorganic salt to form a suspension and thereafter polymerizing the mixture to form colored particles in the range of about 1 to 100 microns, see for example column 4, lines 46 to 55.
In the processes of the prior art, various significant problems exist, for example difficulties in predicting or controlling the bead size of the polymers produced by the reaction are encountered. Moreover, the reactions often produced polymeric fouling, that is undesirable deposits of polymer on the agitator, baffles, heating coils and reactor walls. In some situations, the suspension would coalesce during the reaction. This produced large deposits of undesirable polymeric material which were difficult, expensive and hazardous to remove from the reactor.
Further, polymeric fouling or gel body formation may result in a broad particle size distribution, for example from about 1 to about 500 microns; a large quantity of fines, for example, 20 weight percent of the product beads, that is small size bead particles of less than 100 microns in diameter; and/or difficulties encountered during filtering, and drying and manipulating the product resin beads.
Another problem associated with the prior art suspension agents, such as tricalcium phosphate, used in bead suspension polymerizations is that an additional aqueous acid washing step or steps may be required to remove the residual inorganic salts from the surface of the beads. In certain instances, if the acid washing step is omitted, the performance of the polymer resin in a product application, for example in an electrophotographic toner composition, may be adversely affected, for example in triboelectrification charge properties and melt rheology properties. The aqueous solution of the tricalcium phosphate and acid must subsequently be disposed of requiring an additional processing cost.
These and other disadvantages are avoided, or minimized with the processes of the present invention.
Thus, there remains a need for processes for the preparation of polymeric resin beads by suspension polymerization techniques and which polymers retain many or all of their desirable physical properties, for example hardness, processability, clarity, high gloss durability, and the like, while avoiding the problems of gel formation, purification and performance of the polymer resin bead product associated with the prior art suspension polymerization methodology.